The Optimized Link State Routing Protocol (OLSR) is a proactive routing protocol for ad hoc networks. It uses multipoint relays (MPRs) to reduce flooding of broadcast messages. Each node selects MPRs among its one-hop neighbors that can reach all of its two-hop neighbors. Only MPRs forward broadcast messages to reduce overhead. Nodes declare their MPR selections via topology control messages to help other nodes build routing tables and select routes. This allows OLSR to benefit from the stability of link-state routing while reducing control message flooding through selective use of MPRs.

1. Yuyan Xue OLSR Protocol 1
Optimized Link State Routing
Protocol for Ad Hoc Networks
Presented by Yuyan Xue

2. Yuyan Xue OLSR Protocol 2
Overview
The Optimized Link State Routing Protocol (OLSR) is a
table driven, proactive protocol, i.e., exchanges topology
information with other nodes of the network regularly.
Each node selects a set of its neighbor nodes as "multipoint
relays" (MPR).
Only nodes, selected as such MPRs, are responsible for
forwarding control traffic, intended for diffusion into the
entire network.

3. Yuyan Xue OLSR Protocol 3
Feature
Inherit Stability of Link-state protocol
Multipoint Relays (MPR) employed for
selective flooding
Control traffic by reducing the number of
transmissions required.

4. Yuyan Xue OLSR Protocol 4
Protocol Operation
Neighbor Sensing
MPR Selection
MPR Information Declaration
Routing Table Construction

5. Yuyan Xue OLSR Protocol 5
Neighbor Sensing – Hello Message
 Each node periodically broadcasts Hello message:
 List of neighbors with bi-directional link
 List of other known neighbors.
 Hello messages permit each node
to learn topology up to 2 hops
 Based on Hello messages each
node selects its set of MPR’s

6. Yuyan Xue OLSR Protocol 6
MPR Selection
 Each node select a set
of MPR Selectors
 Who can be a MPR Selectors
of node N ?
- one-hop neighbors of N
 MPR set of Node N (Rules)
(1) Set of MPR’s is able to
transmit to all two-hop neighbors
(2) Link between node and it’s MPR is
bidirectional.
D
S
B
M
X
Y
Z
A

7. Yuyan Xue OLSR Protocol 7
MPR Selection – Con.
Node 1 Hop Neighbors 2 Hop Neighbors MPR(s)
B A,C,F,G D,E C
 Node B will select C as its
MPR So all the other nodes know
that they can reach B via C
30
100
50
110
25
60
10
40
5
10
 D->B route is D-C-B, whose
bottleneck BW is 3 ( Not BW
optimal)
3

8. Yuyan Xue OLSR Protocol 8
MPR Information Declaration
 Topology Control Message (TC)
 Send if there are updates
 Contains:
 MPR Selector Table
 Sequence number
 Topology Table
 Each node maintains a Topology Table based on TC
messages
 Routing Tables are calculated based on Topology tables

9. Yuyan Xue OLSR Protocol 9
Routing Table Construction
 Each node maintains a routing table to all known
destinations in the network
 Routing table:
 Destination address
 Next Hop address
 Distance
 Routing Table is calculated from Topology Table and
recalculated after every change in neighborhood table
or in topological table

10. Yuyan Xue OLSR Protocol 10
References
 G. Pei, M. Gerla, and X. Hong, " LANMAR: Landmark Routing for
Large Scale Wireless Ad Hoc Networks with Group Mobility," In
Proceedings of IEEE/ACM MobiHOC 2000, Boston, MA, Aug. 2000.
 Thomas Clausen, Philippe Jacquet, " Optimized Link State Routing
Protocol (OLSR) ," IETF Internet Draft , July 3 2003.
 X. Hong, K. Xu, and M. Gerla, " Scalable Routing Protocols for
Mobile Ad Hoc Networks " IEEE Network Magazine, July-Aug,
2002, pp. 11-21